Prediction of formation plugging damage that occurs while drilling wells is an important factor in optimizing an oil field's development. The economic impact of near-wellbore drilling-induced damage and cleanup efficiency has led to significant progress in both experimental and numerical studies in order to assess wellbore flow properties during oil production.
The possibility of causing formation permeability plugging damage exists during operations throughout the life of the well. Wellbore damage can cause a reduction in the natural capability of a reservoir to produce its fluids, such as a decrease in porosity or permeability, or both. Damage can occur near the wellbore face which can be relatively easy to repair or deep into the rock which may be difficult to repair.
Damage can occur when sensitive formations are exposed to drilling fluids. Formation plugging damage in a wellbore is generally caused by several mechanisms which can include the following:
1. physical plugging of pores by drilling mud solids;
2. alteration of reservoir rock wettability;
3. precipitation of insoluble materials in pore spaces;
4. clay swelling in pore spaces;
5. migration of fines into pore throats;
6. introduction of an immobile phase; and
7. emulsion formation and blockage.
In well completions, there are several recognized damage mechanisms, such as the invasion of incompatible fluids swelling the formation clays, or fine solids from dirty fluids plugging the formation matrix. Because damage can significantly affect the productivity of any well, adequate precautions should be taken to avoid such damage during all phases in the life of a well.
Natural or induced impairment to production can develop in the reservoir, in the near-wellbore area, or the perforations. Natural damage occurs as produced reservoir fluids move through the reservoir, while induced damage is the result of external operations and fluids in the well, such as drilling, well completion, workover operations, or stimulation treatments. Some induced damage triggers natural damage mechanisms. Natural damage includes phenomena such as fines migration, clay swelling, scale formation, organic deposition, including paraffins or asphaltenes, and mixed organic and inorganic deposition. Induced damage includes plugging caused by foreign particles in the injected fluid, wettability changes, emulsions, precipitates, or sludges caused by acid reactions, bacterial activity, and water blocks. Wellbore cleanup or matrix stimulation treatments are two different operations that can remove natural or induced damage. Selecting the proper operation depends on the location and nature of the damage.
The current practice to shut off a water zone requires a rig to case and cement the entire open-hole and to selectively perforate the oil zone while isolating and maintaining the water zone behind the casing and cement.
In general, formation plugging is considered to be an undesirable phenomenon. The problem to be addressed by the present disclosure is how to utilize these phenomena to plug the porosity and to kill the permeability of a water zone and to retain the oil productive zone in an open hole to allow flow to the wellbore.